Synchronizing and sharing data between multiple endpoints may be accomplished in a variety of ways. In some implementations, synchronization of data may be implemented, at least in part, by the addition of data, such as synchronization data, to a feed that contains data items. For example, one endpoint might publish a feed that contains data items. Another endpoint, or more than one other endpoint, might subscribe to the feed and be notified when, for example, new items are added or existing items are changed. In addition, a subscribing endpoint might publish its own feed, with the same data as is provided in the original publisher's feed and also with changes or additions made by the subscriber. The original publisher might then subscribe to this second feed. Through these mutual subscriptions, and using synchronization data or information in the shared feeds, changes made by either endpoint may be reflected in the data maintained by both endpoints. Other techniques may also be used, including, for example, procedures for operating with conflicts that might occur, for example, when multiple endpoints change the same item independently.
When data sharing and synchronization is implemented as previously introduced, or when it is implemented in at least some other manners, each endpoint that shares data in a synchronization relationship may want to ensure that a feed that the endpoint publishes conforms to an organization or layout required by the synchronization procedures or techniques. For example, to add a new item to a feed, an endpoint may want to add both information about the item and also add synchronization data associated with the item. If the resulting feed does not conform to one or more particular standards or requirements—perhaps if the correct synchronization data is not added, or if the synchronization data is not formatted or provided in the feed in the correct way, and so on—a variety of problems may occur, including in some cases an inability to share or synchronize the new item. A desire to produce a feed that conforms to a required organization or layout may also be applicable for other types of operations, including modifying existing items, deleting existing items, and so on.